1. Field of the Invention
The present invention relates to apparatus for purifying contaminated liquids and more particularly to an apparatus for electrochemical purification of contaminated liquids.
The invention may be employed for purifying liquids contaminated with organic substances, mechanical suspensions, surfactants, and the like.
The invention is particularly useful for purifying liquids contaminated with polymers and petroleum products, such as waste waters containing oils and greases.
2. Description of the Prior Art
Of all the known devices for purifying contaminated liquids, the widest and ever increasing application has recently been found by apparatus for electrochemical purification of liquids, in particular those where liquid is purified by the electroflotation and electrocoagulation methods, which is due to their high performance capabilities.
Apparatus are known where the electrochemical liquid purification process is accomplished either in batches, or continuously; the latter appears to be more promising.
A prior art apparatus for electrochemical purification of contaminated liquids (USSR Inventor's Certificate No. 407,844) comprises a settling chamber communicating with an electrocoagulation chamber installed therewithin. The electrocoagulation chamber has soluble electrodes and an inlet pipe to feed contaminated liquid, disposed below the electrodes; the settling chamber has an outlet pipe to discharge purified liquid. In the course of purification, the contaminated liquid with electrolyzing additives (HCl, NaCl) passes through the soluble electrodes whereto electric current is applied. This brings about the formation of hydroxides of the soluble electrode metal, which coagulate impurities contained in the liquid being purified. From the electrocoagulation chamber, the liquid passes into the settling chamber where foam and sludge separate from the liquid, whereupon the foam, the sludge, and the liquid are discharged separately.
Passing between the electrodes, the liquid being purified fouls these, which accelerates passivation of the electrodes and, hence, increases the power consumption, impairs the purification quality, and necessitates frequent cleaning of the electrodes, i.e. eventually reduces the efficiency of the apparatus.
In another prior art apparatus (Japanese Pat. No. 52-14397, published Nov. 3, 1977), the electrocoagulation chamber serves only to produce coagulants, for which purpose pure electrolyte is fed thereinto, while liquid purification is accomplished in another chamber whereinto the liquid being treated is fed and where the liquid is mixed with the electrolyte containing coagulants and fed from the electrocoagulation chamber.
While greatly diminishing the fouling of the electrode surfaces, such a construction of the apparatus considerably less utilizes the coagulating and flotation capabilities of the electrodes, since in the course of the electrolyte flow from the electrocoagulation chamber to the settling chamber the coagulants (hydroxides of the soluble electrode metal) and gas bubbles originating on the soluble electrode surface aggregate, which reduces their specific surface and, hence, impairs the coagulating and flotation capabilities, and ultimately results in a wasteful expenditure of electric power. Furthermore, an additional electric power is spent for mixing the contaminated liquid with the electrolyte.
Known in the art are apparatus which do not require additional power consumption for the mixing, wherein the contaminated liquid is mixed with the electrolyte in one electrocoagulation chamber, the contaminated liquid being fed into the chamber through an inlet pipe disposed above the electrodes, and the electrolyte being passed between the electrodes.
The liquid purification in such apparatus involves no fouling of the electrodes and proceeds at a higher degree of utilization of the coagulants and gas bubbles and consequently at a higher rate than in the previously described apparatus. For example, an apparatus for electrochemical purification of contaminated liquids, disclosed in USSR Inventor's Certificate No. 644,738, comprises a settling chamber with an outlet pipe to discharge purified liquid, which communicates with a tubular electrocoagulation chamber installed therewithin and having a system of soluble electrodes disposed in its bottom portion and an inlet pipe to feed contaminated liquid, disposed above said system of soluble electrodes. In accordance with the invention under consideration, the inlet pipe to feed contaminated liquid should be spaced from the electrodes at such a distance which excludes the possibility of fouling the latter by impurities contained in the contaminated liquid; for example, with a cylindrical inlet pipe, the distance is of (1 to 7)d, where d is the inlet pipe diameter.
The chief disadvantage of the above-described apparatus lies in that turbulization of electrolyte currents causes coagulants and gas bubbles in the electrocoagulation chamber space between the inlet pipe to feed contaminated liquid and the electrodes as well as in the interelectrode space to aggregate; hence, in this apparatus, as in the previously described one, a considerable amount of electric power is wasted due to incomplete utilization of the coagulants and gas bubbles.